Electrode support and spacing structure for electron discharge devices



A ril 19, 1960 N. c. WITTWER, JR 2,933,636

ELECTRODE SUPPORT AND SPACING STRUCTURE FOR ELECTRON DISCHARGE DEVICES 2Sheets-Sheet 1 Filed Dec. 31, 1956 FIG.

mvzawron N. C. W/TTWER, JR.

Apnl 19, 1960 N. c. WITTWER, JR 2,933,635

ELECTRODE SUPPORT AND SPACING STRUCTURE FOR ELECTRON DISCHARGE DEVICESFiled Dec. a1, 1956 2 Sheets-Sheet 2 FIG. 3

INVENTOR N. C. WI TTWER, JR.

yam c. mm

United States PatentOfitice 2,933,636 Patented Apr. 19, 1960 ELECTRODESUPPORT AND SPACING STRUC- TURE FGR ELECTRON DISCHARGE DEVICES Norman C.Wittwer, Jr., Oldwick, N.J., assignor to Bell Telephone Laboratories,Incorporated, New York, N .Y., a corporation of New York ApplicationDecember 31, 1956, Serial No. 631,611

6 Claims. (Cl. 313-357) This invention relates to electron dischargedevices and, more particularly, to electrode assemblies for electrondischarge devices.

In planar electrode devices having inter-electrode spacings of the orderof 0.001 inch, the problem of attaining the desired spacings is adiflicult one. Another diflicult problem, the desired spacings havingbeen attained, is that of preventing permanent distortion of theelectrodes when the assembly of which they are a part is subjected toshock, physical impact, severe vibration, or temperature change.

With a control grid to cathode spacing in an electron discharge deviceof the magnitude of 0.001 inch, a change in the spacing or a variationin the spacings of the diiferent areas of the electrodes of only 0.0001inch may cause a pronounced change in the transconductance of the deviceand a consequent failure to meet the required performancecharacteristics.

To minimize inter-electrode spacing changes due to permanent distortionresulting from shock, impact and vibration, the electrodes must be asrugged and stable as possible. However, it is not practicable to mountthe electrodes in an absolutely rigid support structure because of thetendency of the electrodes to expand when heated. Rigid mounting andthermal expansion could combine to cause buckling and/ or bowing of thecathode and, as a result, spacing changes and variations. Thus, while aplanar electrode mounting structure must provide secure electrodesupport, it must also, in many applications, allow for longitudinalmovement of portions of the cathode in response to temperature changes.

An object of this invention is to improve electrode mounting structures.

More specifically, an object of the present invention is to maintainaccurately determined electrode spacings during the entire life of anelectron discharge device.

A further object of this invention is to allow substantiallyunrestricted expansion and contraction of portions of a planar electrodein an electron discharge device, thereby accurately maintaining thespacings between it and other electrodes.

Another object of this invention is an electrode supporting structurewhich, while allowing substantially unrestricted expansion andcontraction of portions of a planar electrode, securely anchors otherportions thereof so as to prevent longitudinal displacement of theentire cathode.

A still further object of the present invention is an electrodesupporting structure which is sturdy and readily assembled.

These and other objects are attained in one specific illustrativeembodiment of this invention wherein in an electron discharge device thespacings between a planar cathode and two grids associated therewith areaccurately maintained. The planar cathode assembly, the grid assemblies,and a plate assembly are mounted between and supported by apertured micamembers. The etfective surfaces of the electrodes lie in planes whichare parallel to each other and which are perpendicular to the planes inwhich the micas are positioned.

The control grid assembly, which is located directly adjacent to thecathode, comprises a grid frame upon which are wound a plurality ofturns of fine wire. The grid frame extends through apertures in the micaassemblies and provides projecting portions against which to positionspacer pins. The spacer pins are loaded or biased against the projectingportions of the control grid frame by the assembly of the second grid orscreen grid which includes loading springs. The control grid frameprojecting portions are stepped or ground fiat an amount equal to thedesired cathode to control grid spacing, the cathode being biasedagainst the spacer pins, which rest against the stepped portions, andthe wires of the control grid being wound over unstepped portions of thecontrol grid frame assembly.

The cathode biasing arrangement includes a connection rod assembly whichis securely mounted between the mica members. The connection rodassembly comprises a support rod and a coil spring wound thereon, thespring and support rod being positioned closer to one mica member thanto the other. Each end of the coil spring bears against a cathodeloading pin, a slot in each loading pin receiving a spring end andproviding for secure pin engagement therewith.

The cathode loading pins bear against the cathode and, thus, resilientlyload it against the spacer pins. Because of the off-center positioningof the support rod and coil spring, the cathode loading pins exertunequal forces against different portions of the cathode. Accordingly,when the cathode is heated and forced to expand, only its more lightlyloaded end will move with respect to the spacer pins. Thus, securelongitudinal positioning of the entire cathode is attained.

Furthermore, the sticking force between the cathode and the lightlyloaded pin is less than the sticking forces present in a cathodeassembly having a centrally positioned support rod and coil spring.Thus, the minimum force that must be overcome by portions of the cathodein longitudinally moving in response to temperature changes is less inillustrative embodiments of the present invention than in electrodeassemblies as heretofore constructed. As a result, buckling and bowingand spacing changes and variations caused thereby are substantiallyreduced.

Accordingly, a feature of the present invention is a planar cathode,portions of which are equally and resiliently biased against spacer pinsby an off-center coil spring assembly.

A further feature of this invention is an electrode assembly including aconnection rod assembly comprising an off-center support rod havingwound thereon a coil spring, the ends of which unequally bear againsttwo cathode loading pins, thereby anchoring the more heavily loadedcathode portion to the pin which it contacts and allowing substantiallyfree expansion and contraction of those portions of the cathode whichcontact the other loading pin.

A complete understanding of this invention and of the various featuresthereof may be gained from consideration of the following detaileddescription and the accompanying drawing, in which:

Fig. 1 is an elevational view of an electrode assembly constructed inaccordance with the principles of the. present invention;

Fig. 2 is an end view of the assembly of Fig. 1; and

Fig. 3 is a perspective view of a portion of the assembly of Fig. l. V j

Referring now to the drawing, Figs. 1 and 2 show 4 an electrodeassemblyillustrative of the principles of this invention and which may be easilyarranged, mounted openings 12 and 13 have gridframe members or rods,

14 and 15 respectively, extending therethrough, grid crossframe members16 and 17 being attached to the members 14 and 15 in any suitable mannerthereby formiug a rigid grid-frame assembly. in one illustrativeembodiment of this invention 77G turns per inch oflkOOGZS inch diametertungsten wirewere laterally wound on the grid frame members ,14 and 15to form a control g'idelectrode.

A screen grid assembly is positioned'between the micas 10 and 11 and inclose proximity to the above-mentioned control grid. The screen gridcomprises a screen frame member 18 having 135 turns per inch of 0.001inch 7 diameter tungsten wire wound thereon. Thegframe member 18includes tab elements 19 which extend through the mica assembly openings12 and 13 and rest-onspacer pins 20. The spacer pins 2%) areadvantageously made of a ceramic material and must be straight within10.091 inch. Loading spring assemblies 21 serve to hold the screen gridsecurely in place, and also serve to bias the spacer pins 20, the pinsresting on, the grid frame members '14 and 15. The loading springasscmbliesinclude clip elements ,211 which are. intended toholdthespacer pins 26 against the mica assemblies 10, and 11. A coatedcathode 23 is biased against the spacer pins 20 by an assembly includingloading pins 32 and 33. As seen in Fig. 3, the non-emitting face ofthe-cathode 23 contains two openings therethrough for the-pins '32 and33.

As seen in Figs. 1 and 2,the' portions of the grid frame members 14 and'15 which project beyond the mica assemblies 10 and 11 are stepped, thesteps or flat portions being in contact with the spacer pins 2%. Sincethe lateral grid wires are wound over unstepped portions of the framemembers 14 and 15, the amount or depth of the step determines thespacing between the emitting surface of the cathode 23 and thelowersurface defined by the lateral grid wires. The depth of the steppedportions, and thus the cathode-control grid spacing, can, of course, byvery accurately determined in, for example, a grinding operation. For amore detaile'd'description of this type ofspacing means, reference maybe made toPatent 2,663,819, C. T. Goddard, December'22, 1953. Thecathode biasing assembly comprises'connection rods 24 and a supportrod'25. The center of thesupport rod 25 is positioned closer to the micaassembly 11 than tothe assembly 10. The rod 25 is advantageouslyattached to the connection rods 24 by welding.

The connection rods'24 extend through the micas 10 .and 11 and throughguide plate members 27 and 23. Each connection rod 24 has two fixedwashers 29 thereon. The washers .29 contact the micas 1t) and 11 and incombination with eyelets 3i securely position the rods '24 with respectto the micas 19 and 11.

The guide plates 27 and 28 contain connection rod receiving openingstherethrough, and are secured in place by the eyelets "39'and tne-rnicas1G and 11. Furthermore, 7

each guide plate contains a'genera'lly cylindrically shaped guideportion 31.

Cathodejloading pins '32 and 33rest in the gu ideportions 31 and arebiased against'the cathode "23 by the .ends of a coil spring 34 which iswound on the oil-center support rod 25. Each cathode loadingipinincludes a slotted lower portion which is designed "to engage one of thecoil spring ends. The spring ends can be arranged to impinge-upon theslotted ends of the loading pins 32 crimping. V

micas and prevent the anode 36 from rotating about the cathode.

. Id and 33 by oblique positioning of the support rod 25 on theconnection rods 24.

The loading pins 32 and 33 extend through the guide portions 31 of theplates 27 and 28 and resiliently bear against the cathode 23. As seen inFig. 3, the openings in the non-emitting face of the cathode 23 receivethe pins 32 and 33 and allow them to rest against the inside surface ofthe emitting side of the cathode 23. The openings, inproviding passagesfor the loading pins to extend through the back or non-emitting face of;the cathode, eliminate the cathode crushing or squashing which commonlyresults if the pins are loaded against'the nonemitting cathode face.Such crushing causes the cathode to bow toward the grid; the bowingconstitutes an un- 10 and 11 and is supported on an assembly rod 57.The:

ends of the rod 37 extendthrough. the micas and have fitted thereontubular eyelets 38, the'eyelets being secured to the rod 37 in anysuitable manner as, for example, by Anode tabs 39 fit through openings4% in the assembly support rod 37.

The illustrate and described electrode assembly, while beingmechanically rugged and stable, exhibits sufiicient flexibility tomaintain accurately determined electrode spacings over a considerablerange of temperature during the entire life of an electron dischargedevicel The lightly loaded cathode pin, i'.e., pin 32-, offers a minimumconstraint or sticking force to the tendenc of the cathode portion whichit contacts to expand or contract in response to temperature changes,while theother cathode loading pin, i.e., pin 33, bears against thecathode 23with sutficient force to prevent longitudinal movement lofthecathode portion which it contacts. Thus, 33- anchors a portion or thecathode 23 and prevents'the entire cathode from longitudinally slidingor Walking. Gn the other hand, the lightly'loaded .pin 32' is designedso that the small force with which it bears against a portion of thecathode 23 does not significantly interfere with longitudinal shiftingof that portion of the cathode in'response to temperature changes. Thus,provlsion'is made for substantially free thermal expansion.and-contraction of the cathode in a direction perpendicular to the micaassemblies so that cathode buckling and bowing and electrode spacingchanges caused thereby are markedly reduccd.

It is to be understood that the above-described em merous otherarrangements may be madeby those skilled' in the art without departingfrom the spirit and scope of this invention.

What is claimedis: v a

l. An electrode assembly comprising a planar cathode, a control grid,said control grid comprising two parallel rods and aplurality of turnsof wire wound on said rods, spacer members disposed erpen'dicular to andin contact with said rods, two pins bearing laterally against respectiveopposite ends of saidcathode, and means for spring-loading said pinssuch that oneis more heavily loaded than the other, said planar cathodebeing biased against said spacer members by said pins, whereby theportion of said cathode in contact with the more heavily l'oaded pinremains stationary withrespect thereto, while the portion ofsaidjcathode in contact with the less'heavily loaded pin is free to movelongitudinally in response to temperature induced expansions'andcontractions of said 2. In combination, an elongated fiat cathode,spacer members respectively disposed in contact withl end portions-ofsaid cathode, and means laterally brasingtheend portions of said cathodeagainst said spacer members with respectively diderent forces.

3. In combination, a fiat cathode, a spacer member in contactrespectively with a portion of each end of said cathode, and meanslaterally biasing said end portions against said members withrespectively different forces, said means comprising biasing pins andspring means, each of said biasing pins being in contact with an endportion of said cathode and said spring means being positionedoff-center with relation to said biasing pins and in contact therewith,such that a greater force is exerted on one than on the other of saidpins.

4. An electrode assembly for an electron discharge device comprising aflat elongated cathode, a control grid adjacent the emissive surface ofsaid cathode, spacer members at each end of said cathode and defin ngthe spacing between said emissive surface and said control grid, a pinbearing laterally against said cathode at each end thereof, and meansspring biasing one of said pins against said cathode more heavily thanthe other of said pins, said means including .a spring having a firstportion biasing said one pin and a second portion biasing said other pinand means positioning said spring closer to said one pin than to saidother pin.

5. An electrode assembly for an electron discharge device comprising aflat elongated cathode, spacer means in contact with opposite ends ofone surface of said cathode, and means laterally biasing said oppositeends of said cathode against said spacer means with different forces,said biasing means including loading members bearing against the othersurface of said cathode at said opposite ends and spring means moreheavily loading one of said loading members than the other of saidloading members.

6. An electrode assembly in accordance With claim 5 wherein spring meansincludes a spring member having end portions bearing against saidloading members and means positioning said spring member closer to saidone loading member than said other loading member.

References Cited in the file of this patent UNITED STATES PATENTS

